Thermo-mechanical simulations of LTCC packages for RF MEMS applications

Stresses and strains in assemblies of a silicon-based MEMS chip and in an LTCC package have been simulated using Comsol Multiphysics simulation software. The simulated structures included the MEMS chip either wire bonded or flip-chip bonded into a cavity in a LTCC substrate and an LTCC lid sealed on top of the cavity. For die bonding of the MEMS chip and for sealing of the lid AuSn solder material was assumed and for the flip-chip joining of the MEMS chip Au-bumps and thermo compression bonding process were assumed. Both 2D and 3D simulations were made for a temperature range between 218 K and 393 K, for pressures up to 100 bar, for shear force applied either to chip or lid edge and for heat dissipation of 1 W applied to the chip. The effects of 2^nd level packaging were also studied. The simulations show that the strains at the surface of the MEMS components are larger in the flip-chip type chip compared with wire bonded chip. For thermal management of the LTCC type package thermal vias through the LTCC substrate will be necessary. Several possible ways for minimizing the strains in the MEMS component are discussed in this article.